11. Maintaining Fleet Batteries 2

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11.1 The ‘Green Light’ Lies

When charging a battery, the ready light will eventually
illuminate, indicating that the battery is fully charged. The user
assumes that the battery has reached its full potential and the
battery is taken in confidence.

In no way does the ‘green light’ guarantee sufficient battery
capacity or assure good state-of-health (SoH). Similar to a toaster
that pops up the bread when brown (or black), the charger fills the
battery with energy and ‘pops’ it to ready when full
(or warm).

The rechargeable battery is a corrosive device that gradually
loses its ability to hold a charge. Many users in an organization
are unaware that their fleet batteries barely last a day with no
reserve energy to spare. In fact, weak batteries can hide
comfortably because little demand is placed on them in a routine
day. The situation changes when full performance is required during
an emergency. Total collapse of portable systems is common and such
breakdowns are frequently related to poor battery performance.
Figure 11-1 shows five batteries in various states of
degradation.

Figure 11-1: Progressive loss of
charge acceptance.The rechargeable battery is a corrosive
device that gradually loses its ability to hold charge as part of
natural aging, incorrect use and/or lack of maintenance. The
unusable part of the battery that creeps in is referred to as ‘rock
content’.

Carrying larger packs or switching to higher energy-dense
chemistries does not assure better reliability if the weak
batteries are not ‘weeded’ out at the appropriate time. Likewise,
the benefit of using ultra-advanced battery systems offers little
advantage if packs are allowed to remain in the fleet once their
performance has dropped below an acceptable performance level.

Figure 11-2 illustrates four batteries with different
ratings and SoH conditions. Batteries B, C and D show reduced
performance because of memory problems and other deficiencies. The
worst pack is Battery D. Because of its low charge acceptance, this
battery might switch to ready after only 14 minutes of charge
(assumed time). Ironically, this battery is a likely candidate to
be picked when a fresh battery is required in a hurry.
Unfortunately, it will last only for a brief moment. Battery A, on
the other hand, has the highest capacity and takes the longest to
charge. Because the ready light is not yet lit, this battery is
least likely picked.

Figure 11-2: Comparison of charge and
discharge times.This illustration shows typical charge
and discharge times for batteries with different ratings and SoH
conditions. Carrying larger batteries or switching to high
energy-dense chemistries does not necessarily assure longer runtime
if deadwood is allowed to remain in the battery fleet.

The weak batteries are charged
quicker and remain on ‘ready’ longer than the strong ones. The bad
batteries tend to gravitate to the top. They become a target for
the unsuspecting user. In an emergency situation that demands quick
charge action, the batteries that show ready may simply be those
that are deadwood.

A weak battery can be compared to a fuel tank with an
indentation. Refueling this tank is quicker than a normal tank
because it holds less fuel. Similar to the ‘green light’ on a
charger, the fuel gauge in the vehicle will show full when filled
to the brim, but the distance traveled before refueling will be
short.